1. Field of the Invention
The present invention relates to a telecine apparatus and, more particularly, to a telecine apparatus of an equal-interval pull-down system in which a film can be pulled down at low speed.
2. Description of the Prior Art
A word "telecine" is a compound word of television and cinema and generally refers to an apparatus which converts a film image of movie or the like into a television signal. The present invention defines a telecine apparatus as an apparatus that converts an image information stored in an intermediate material into a video signal.
Japanese Laid-Open Patent Publication No. 58-182384 describes in detail a conventional telecine apparatus. FIG. 1 of the accompanying drawings shows a block diagram of a conventional telecine apparatus serving as a three-tube film image pickup apparatus.
As shown in FIG. 1, there is provided a film projector 1 which includes a 16-mm film that was already photographed and a film pull-down mechanism which will be described later on. An image information from the film projector 1 is projected through a lens 2 onto a spectral system 3. The spectral system 3 includes a shutter 4 that interrupts the film image information projected from the film projector 1. The shutter 4 is driven by a drive motor (M) 5. Further, the spectral system 3 includes a dichroic mirror (not shown) by which an incident light is analyzed into three primary colors of R (red), G (green) and B (blue) and projected onto a picture screen of a camera tube 6 such as Saticon or the like for three primary colors R, G and B.
Film image informations, photoelectrically converted by the camera tubes 6R, 6G, 6B for three primary colors R, G, B, are respectively applied to pre-amplifiers 7R, 7G and 7B, in which they are enhanced in S/N (signal-to-noise) ratio and then supplied to process-amplifiers 8R, 8G and 8B, respectively. The process-amplifier 8 processes the image informations in a predetermined processing fashion such as mixing of blanking, black level clipping, gain control, pedestal level adjustment, shading correction, gamma correction or the like. Then, the image informations thus processed by the process-amplifiers 8R, 8G, 8B are supplied to an encoder or the like and are thereby converted into an NTSC television video signal.
A standard speed of the 16-mm film or the like, for example, is 24 frames per second and is slow as compared with that of the NTSC television system in which 30 pictures (60 fields) are transmitted and displayed per second. Therefore, if the film frame number is converted into a television picture as it is, then a noise such as a so-called shutter bar or the like appears.
To avoid such a drawback, the conventional telecine apparatus adopts a special intermittent driving method. More specifically, during the film is in motion, the shutter 4 is closed to interrupt the light from the film projector 1. Then, the film is transported so that the shutter 4 is opened when the film is not in motion. Then, a still picture information of film is picked up by the camera tube 6. Accordingly, a relation between the radiation of light on the film and the field of the television picture is set as 1/24 (second).times.2 frames=1/60.times.5 fields=1/12 (second), i.e., during 1/12 second, 2 frames of the film correspond to 5 fields of the television video signal.
As a pull-down system for intermittently moving the film so that the film is pulled down, there are known an equal-interval pull-down system and a 2-3 pull-down system.
The equal-interval pull-down system will be described with reference to FIGS. 2A and 2B. FIG. 2A shows the scanning state of the standard television system such as the NTSC television system or the like. As shown in FIG. 2A, 2 frames of the film are pulled down during 1/12 second of first to fifth fields. As shown in FIG. 2B, a pull-down period, i.e., P interval occurs at every 2.5 fields of the television video signal. When the film is not in motion, a light from the light source (not shown) is radiated five times per frame by means of recesses or slits formed on the disk of the shutter 4 so that 24 frames of the film and 30 pictures per second of the standard television system are made coincident with each other.
The shortcomings of this equal-interval pull-down system are such that a radiation time is short and that a pull-down speed of the film is high. There is then the problem that perforations of the film will be easily damaged. The 2-3 pull-down system is proposed in order to improve this disadvantage.
According to the 2-3 pull-down system, the pull-down of film is carried out such that, as shown in FIG. 2C, an odd frame is transported in 1/30 second and an even frame is transported in 1/20 second within 1/12 second cycle. More specifically, in FIG. 2C, a hatched portion P represents a pull-down operation portion, a portion C represents a vibration period following the pull-down operation and a blank portion e represents a radiation portion. Odd frames 1, 3, 5, . . . of the film correspond to 2 fields of the NTSC television video signal or the like. Even frames 2, 4, 6, . . . are pulled-down at every 24 frames per second in response to 3 fields of the NTSC television video signal or the like.
FIG. 2D shows the reading state of fields of the television video signal. As shown in FIG. 2D, a first frame A of odd frame of the film is pulled down to an odd field AO and an even field AE of the television video signal, and a second frame B of even frame of the film is pulled down to an odd field BO, an even field BE and an odd field BO of the television video signal. Similarly, a third frame C of an odd frame is pulled down to an even field CE and an odd field CO of the television video signal, and a fourth frame D of an even frame is pulled down to an even field DE, an odd field DO and an even field DE of the television video signal.
According to the above-mentioned 2-3 pull-down system, although the utilization ratio of light is increased as compared with that of the equal-interval pull-down system, the frame of the film is pulled down at the ratio of 2:3, causing the film pull-down mechanism to become extremely complicated. Also, a vibration thereof becomes large.
As described above, the 2-3 pull-down system and the equal-interval pull-down system both have merits and demerits. In order to simplify the structure of the pull-down mechanism much more, the present invention adopts the equal-interval pull-down system to enable the pull-down mechanism to be smoothly driven intermittently. Further, according to the conventional equal-interval pull-down system, the radiation of light is carried out once per field to read out electric charges so that the film must be pulled down and the shutter must be opened within one field without fail. There is then the disadvantage that the pull-down speed of the film increases to damage the film.
Furthermore, when the image information of the film is picked up by using the camera tubes 7R, 7G and 7B, a time difference of a little less than one field (1/60 second) occurs in storage time at the scanning starting point (upper portion of picture screen) and a scanning ending point (lower portion of picture screen) because electric charges are read out by the scanning of electron beam on the photoelectric conversion layer. There is then the disadvantage that a subtle timing relation between the shutter and the scanning of electron beam must be adjusted.